1. Technical Field
The present invention relates to a device and technique for measuring or comparing rheological properties and viscosity of multiple samples simultaneously for rapidly screening, characterizing and comparing a library of material samples.
2. Discussion
Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compounds or mixtures commonly known as libraries. Additionally, it refers to techniques and instruments for evaluating or screening libraries for desirable properties. Combinatorial chemistry has revolutionized the process of formulating of mixtures and has enabled researchers to rapidly discover and optimize useful mixtures of materials.
One useful screening criterion is a liquid flow properties. Viscosity is one such property which is a physical property that characterizes a fluid's resistance to flow. For laminar flow of Newtonian fluids, including gases and simple liquids, viscosity is proportional to the tangential component of stress divided by the local velocity gradient. Complex fluids such as pastes, slurries, and polymer solutions do not follow a constant relationship between tangential stress and local velocity gradient. For them rate dependent viscosity, its analogs and other rheological measurements can serve as useful screening criteria.
Rheology is the study of the deformation and flow of fluids under the influence of an applied stress. Stress includes, for example, a shear stress, compressive stress, and extensional stress. The experimental characterization of a material's Theological behaviour is known as rheometry, although the term rheology is frequently used synonomously with rheometry. Experimentalists often refer to the measurement of rheologic properties as quantification of the movement of flowable materials in response to applied stresses. A stress is a force applied over an area.
Combinatorial libraries routinely comprise thousands of individual library members. As a result, most viscometers are unsuitable for screening purposes because they were designed to slowly process one sample at a time. Although generally the throughput of serial measurement techniques can benefit from automation, many viscometers have relatively long response times. These instruments often require time-consuming sample preparation making them impractical for use as screening tools.
U.S. Pat. No. 6,393,898 teaches simultaneously measuring viscosity of multiple samples by timing the flow of each through a sample tube of known dimensions. While this has utility it does not allow the measurement of time dependent rheological properties. It does not allow the acquisition of rheological data at two or more levels of applied stress or the testing of a property multiple times during withdrawal from a sample reservoir. This teaching does not allow visualization and quantification of complex flow patterns.
The present invention overcomes these problems noted above.